1. Field of the Invention
This invention relates to a retractor and anterior cervical plate device for anterior cervical spinal fusion and instrumentation where the device includes retractor support posts mounted to the vertebrae that provide a multi-axial orientation relative to the vertebrae to reduce retraction injury and an integrated anterior cervical plate that facilitates instrumentation placement.
2. Discussion of the Related Art
The human spine includes a series of vertebrae interconnected by connective tissue referred to as intervertebral discs that act as a cushion between the vertebrae. The discs allow for movement of the vertebrae so that the back and neck can bend and rotate.
Neck and arm pain and other related symptoms may occur when a cervical intervertebral disc herniates resulting in compression of the spinal cord and/or nerve roots. A disc herniates when some of the disc's nucleus pulposus bulges or ruptures through the annulus fibrosis. To relieve the symptoms surgeons may perform an anterior cervical discectomy to remove the offending disc material. The intervertebral space is then filled with a piece of bone or a cage filled with graft material to achieve a fusion between adjacent vertebral bodies.
To facilitate the fusion process a plate is often applied that acts to immobilize the segment and allow for bone growth between adjacent vertebral bodies. In order to perform this procedure, the surgeon makes a small incision in the front of the patient's neck to reach the cervical spine. The procedure is relatively pain free since the surgeon approaches the anterior cervical spine between natural muscle plains. The trachea and esophagus are retracted medially and the carotid artery retracted laterally to reveal the disc space.
Retraction injuries can occur since the structure must be retracted significantly for the surgeon to look straight down at the front part of the vertebrae. Additionally, significant retraction is maintained through the entire time of the procedure resulting in the vast majority of these patients waking up with significant swallowing difficulties. Up to 70% of patients undergoing anterior cervical discectomy and fusion will experience some element of swallowing difficulty after this procedure, most likely from retraction of the esophagus since the surgeon is forced to move the esophagus away from the midline. Hoarseness can also result from retraction injury to the recurrent laryngeal nerve.
In addition, the current retractor systems used require the post be inserted into adjacent vertebral bodies in order to distract open the disc space in order to perform the discectomy and place any graft material under compression. The posts are distracted and then the graft material placed into the disc space, releasing the distraction force and allowing for compression of the graft material which promotes bone fusion. The distractor posts are then removed and the anterior cervical plate is placed. Because the initial midline location of the distractor post are lost as well as their ability to expose the anterior cervical spine, the final plate placement is often crooked or off to one side of the spine. The current design takes into consideration that the distractor posts, if properly placed, mark the midline of the vertebral body and can be used to properly align and facilitate anterior cervical plate placement. This could have a detrimental effect of loading sharing forces on the plate and or intervertebral graft material resulting in graft or plate failure. Additionally, the current retractor systems often times slip out of place or rotated during the procedure which can result in injury and even perforation of the esophagus, trachea or carotid artery. It was with these limitations and potential complications associated of the currently used system that the present design was made. The currently described modifications to the anterior cervical retractor system works to reduce retractor related injury to the patient's neck structures and facilitate the surgical exposure. Additionally, the retractor system is designed to facilitate anterior plate placement.